Data communication method and apparatus via interlock between heterogeneous networks in radio access system supporting multi radio access technology

ABSTRACT

The present invention relates to a method for transmitting and receiving data via a first base station supporting a first radio access technology (RAT) and a second base station supporting a second RAT in a radio access system supporting a multi-radio access technology, and the method may include allowing the first base station to perform a registration procedure with the second base station; and allowing the first base station to transmit control information required for accessing the second base station to a terminal supporting multi-RAT (multi-RAT terminal), wherein the control information comprises beacon frame transmission timing information of the second base station, and the beacon frame transmission timing is maintained in transmission timing of a downlink frame or downlink sub-frame of the first base station with relative timing offset interval.

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. §119(e), this application claims the benefit ofU.S. Provisional Application No. 61/430,170, filed on Jan. 6, 2011, thecontents of which are hereby incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a multi-RAT system, and moreparticularly, to a method and apparatus for performing datacommunication via interlock or coordination between heterogeneousnetworks.

2. Description of the Related Art

Multi-RAT Network (or System)

Multi radio access technology (multi-RAT) network is a wirelesscommunication environment in which there exist two or more heterogeneousnetworks, and a terminal can access two or more heterogeneous networksto simultaneously perform communication.

Heterogeneous network (or heterogeneous system) refers to a networkusing a communication scheme which is different from that of a specificnetwork on the basis of the specific network. For example, a WiMAXnetwork which is an example of a mobile communication system and a Wi-Finetwork which is an example of WLAN may be heterogeneous networks withrespect to each other.

Further, RAT is a technology type used in radio access. For example, RATmay include GSM/EDGE Radio Access Network (GERAN), UMTS TerrestrialRadio Access Network (UTRAN), Evolved-UMTS Terrestrial Radio AccessNetwork (E-UTRAN), WiMAX, LTE(-A), WiFi, and the like. In other words,GERAN, UTRAN, E-UTRAN, WiMAX and/or WiFi may be intermixed in the samearea.

In addition, a terminal capable of accessing two or more heterogeneousnetworks to perform communication, i.e., capable of supportingmulti-RAT, may be referred to as a “multi-system terminal” or“multi-mode terminal.”

In recent years, terminals supporting both a cellular network and WLANhave been typically on the market in a broadband wireless communicationsystem. Each system has different characteristics (advantages ordisadvantages), and thus may perform a complementary operation, therebyproviding enhanced services. The following Table 1 illustrates thecharacteristics of a cellular network and WLAN.

TABLE 1 Pros Cons Note WLAN Higher BW Uncontrolled Mobility WLANprovides Low cost for deployment No connection management Higher BW/LowLow overhead for Limited QoS support latency maintaining connectionsHigh power consumption for network Cellular provides Low access delayfor discovery QoS support random access with small Hard to managinginterference Mobility/connection number of MSs Severe performancedegradation with management the large number of MSs Co-ordinates thedevices to connect WLAN Cellular Mobility Management Higher access delayfor scheduled Guaranteed QoS access support Secure Large controloverhead for data transmission transmission

A multi-RAT terminal may typically perform communication via a cellularnetwork, but may also transmit and receive data by using WLAN AP whenthe WLAN AP is located in the vicinity. Even in this case, when WLANcannot support QoS in case of a service in which the QoS should beguaranteed such as a phone service, the multi-RAT terminal may transmitdata via a cellular network. In other words, a multi-RAT terminal canperform data communication using a more excellent network, and in theaspect of a system, high-speed data transmission is dispersed into WLAN,thereby increasing an overall system efficiency.

In other words, according to the related art, a terminal havingcapability supporting two or more heterogeneous networks can performcommunication using different networks, but operates based on a simpleswitching mechanism, thereby having a limit in the efficiency. Forexample, since different networks are operated in an independent manner,the management may be inefficiently carried out in the aspect ofsecurity/authentication, IP flow mobility, network discovery, and thelike.

SUMMARY OF THE INVENTION

An aspect of the present disclosure is to provide a method in which amulti-RAT terminal can simultaneously transmit and receive data via botha cellular network and WLAN.

Furthermore, another aspect of the present disclosure is to provide amethod in which a cellular network and WLAN can transmit and receivedata in coordination (or interlock) with each other. In particular,there is provided a method in which a multi-RAT terminal cansimultaneously transmit and receive data via both a cellular network andWLAN under the control of a cellular network.

In addition, still another aspect of the present disclosure is to definethe structure and operation for an AP (C-AP) of WLAN in coordinationwith a cellular network.

According to the present disclosure, there is provided a method fortransmitting and receiving data via a first base station supporting afirst radio access technology (RAT) and a second base station supportinga second RAT in a radio access system supporting a multi-radio accesstechnology, and the method may include allowing the first base stationto perform a registration procedure with the second base station; andallowing the first base station to transmit control information requiredfor accessing the second base station to a terminal supporting multi-RAT(multi-RAT terminal), wherein the control information comprises beaconframe transmission timing information of the second base station, andthe beacon frame transmission timing corresponds to that of a downlinkframe or downlink sub-frame of the first base station.

Furthermore, the method may be characterized in that the first RAT is aradio access technology supporting a cellular system, and the second RATis a radio access technology supporting a wireless local area network(WLAN).

Furthermore, the method may be characterized in that the first basestation and the second base station are connected to each other overwired or wireless connections.

Furthermore, according to the present disclosure, there is provided amethod for allowing a terminal to transmit and receive data via a firstbase station supporting a first radio access technology (RAT) and asecond base station supporting a second RAT in a radio access systemsupporting a multi-radio access technology, and the method may includeperforming data communication via a first carrier with the first basestation; receiving control information required for accessing the secondbase station from the first base station; performing a scanningprocedure for at least one second base station located in the vicinityof the first base station based on the control information; performingan access procedure with the second base station; and performing datacommunication via a second carrier with the accessed second basestation, wherein the control information comprises beacon frametransmission timing information of the second base station, and thebeacon frame transmission timing is maintained in transmission timing ofa downlink frame or downlink sub-frame of the first base station withrelative timing offset interval.

Furthermore, according to the present disclosure, there is provided amethod for transmitting and receiving data via a first base stationsupporting a first radio access technology (RAT) and a second basestation supporting a second RAT in a radio access system supporting amulti-radio access technology, and the method may include allowing thesecond base station to perform a registration procedure with the firstbase station; allowing the second base station to transmit a beaconframe to a terminal supporting multi-RAT (multi-RAT terminal);performing an access procedure with the multi-RAT terminal; andperforming data communication via a virtual carrier with the multi-RATterminal; wherein a transmission period of the beacon frame correspondsto that of a downlink frame or downlink sub-frame of the first basestation, and the virtual carrier is distinguished from a carrierperforming data communication between the first base station and themulti-RAT terminal.

Furthermore, the method may be characterized in that said performing aregistration procedure includes searching a first base station capableof communicating with the second base station; and registering to thesearched first base station using an MAC message.

Furthermore, the method may be characterized in that informationrequired for an access to the multi-RAT terminal is exchanged with thefirst base station through the step of performing the registrationprocedure.

Furthermore, according to the present disclosure, there is provided aterminal for transmitting and receiving data via a first base stationsupporting a first radio access technology (RAT) and a second basestation supporting a second RAT in a radio access system supporting amulti-radio access technology, and the terminal may include a wirelesscommunication unit configured to transmit and/or receive wirelesssignals to and/or from the outside; and a controller connected to thewireless communication unit, wherein the controller controls to performdata communication via a first carrier with the first base station,controls the wireless communication unit to receive control informationrequired for accessing the second base station from the first basestation, controls to perform a scanning procedure for at least onesecond base station located in the vicinity of the first base stationbased on the control information, controls to perform an accessprocedure with the second base station, and controls the wirelesscommunication unit to perform data communication via a second carrierwith the accessed second base station, wherein the control informationcomprises beacon frame transmission timing information of the secondbase station, and the beacon frame transmission timing is maintained intransmission timing of a downlink frame or downlink sub-frame of thefirst base station with relative timing offset interval.

According to the present disclosure, a frame timing of the cellularsystem may be synchronized with a beacon frame timing of WLAN AP,thereby reducing the power consumption of the multi-RAT terminal todetect an AP.

Furthermore, according to the present disclosure, inter-AP interferencecan be reduced through interlock or coordination between a cellularsystem and WLAN.

Furthermore, according to the present disclosure, data communication canbe dispersed over a cellular system and WLAN, thereby having the effectof reducing an overhead of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIGS. 1A through 1D are conceptual views illustrating a multi-RAT systemto which an embodiment of the present disclosure is applicable;

FIG. 2 is a view illustrating the logical structure of a C-AP accordingto an embodiment of the present disclosure;

FIGS. 3A and 3B are structural views illustrating a multi-RAT systemwhen the C-AP is operated in a wireless backhaul mode;

FIG. 4 is an example of the structural view illustrating a multi-RATsystem when the C-AP is operated in a converged gateway mode;

FIGS. 5A and 5B are structural views illustrating a multi-RAT systemwhen the C-AP is operated in coordinated AP mode;

FIG. 6 is a flow chart illustrating a data communication method of amulti-RAT terminal in a multi-RAT network according to an embodiment ofthe present disclosure;

FIG. 7 is a flow chart illustrating the first embodiment;

FIG. 8 is a flow chart illustrating the second embodiment;

FIG. 9 is a flow chart illustrating the third embodiment; and

FIG. 10 is an internal block diagram illustrating a terminal and a basestation in a multi-RAT system to which an embodiment of the presentdisclosure is applicable.

DETAILED DESCRIPTION OF THE INVENTION

The following technology may be used in various wireless communicationsystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier FrequencyDivision Multiple Access (SC-FDMA), and the like.

CDMA may be implemented with a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implementedwith a radio technology such as Global System for Mobile communications(GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented with a radio technology suchas IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA(E-UTRA) and the like. IEEE 802.16m is an evolution of IEEE 802.16e,providing backward compatibility with an IEEE 802.16e-based system.

UTRA is part of Universal Mobile Telecommunications System (UMTS).

3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) ispart of Evolved UMTS (E-UMTS) using Evolved-UMTS Terrestrial RadioAccess (E-UTRA), employing OFDMA in the downlink and SC-FDMA in theuplink. LTE-Advanced (LTE-A) is an evolution of 3GPP LTE.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings, and thesame or similar elements are designated with the same numeral referencesregardless of the numerals in the drawings and their redundantdescription will be omitted. In describing the present invention,moreover, the detailed description will be omitted when a specificdescription for publicly known technologies to which the inventionpertains is judged to obscure the gist of the present invention. Also,it should be noted that the accompanying drawings are merely illustratedto easily explain the concept of the invention, and therefore, theyshould not be construed to limit the concept of the invention by theaccompanying drawings. The concept of the invention should be construedas being extended to all modifications, equivalents, and substitutes inaddition to the accompanying drawings.

Hereinafter, a method in which a multi-RAT terminal transmits andreceives data via coordination (or interlock) between heterogeneousnetworks in a multi-RAT network proposed by the present disclosure willbe described in detail.

FIGS. 1A through 1D are conceptual views illustrating a multi-RAT systemto which an embodiment of the present disclosure is applicable.

As illustrated in FIGS. 1A through 1D, a multi-RAT network 100 mayinclude a primary system 110 and a secondary system 120.

The primary system 110 may include a multi-RAT terminal 10, a first basestation 20, and a second base station 120. Furthermore, the primarysystem may refer to a system which always has a status with themulti-RAT terminal. In other words, the primary system may refer to asystem maintaining an activated state, a sleep mode state or an idlemode state with the multi-RAT terminal.

The secondary system 120 may include a multi-RAT terminal 10 and asecond base station 30.

Furthermore, the secondary system may refer to a system that can beadded or removed to or from a multi-RAT network as occasion demands.Furthermore, the secondary system may be mainly used to transmit andreceive data requiring a higher bandwidth (BW). Accordingly, a specificflow (QoS) may be mapped to use the secondary system. Here, the basestation of the secondary system, namely, the second base station, mayoperate in a similar manner to a terminal having the capability ofperforming communication with the primary system.

The primary system and secondary system may be operated in interlockwith a provider's network. The primary system 110 and secondary system120 may be expressed as a primary network and secondary network,respectively. Hereinafter, for the sake of brevity of explanation, theprimary system represents a “cellular system”, and the secondary systemrepresents “WLAN”, for example.

Furthermore, a base station (first base station) corresponding to thecellular system and a base station (second base station) correspondingto the WLAN will be expressed as an “ABS” and an “AP”, respectively.Furthermore, an access to the cellular system and to the WLAN may denotean access to an ABS and to an AP, respectively.

Referring to FIG. 1A, a cellular system and WLAN may be interlocked withthe same core network via each gateway (WLAN Access Gateway (WAG),Access GW (SGSN)). In other words, the multi-RAT terminal cansimultaneously transmit and receive data via both a cellular system andWLAN having the same core network.

Furthermore, referring to FIGS. 1B through 1D, a cellular system andWLAN may be connected via a wired connection (backhaul controlconnection; FIG. 1B) or wireless connection (Over-The-Air (OTA); FIG.1C/1D) in a multi-RAT network to be in coordination or interlock witheach other. In other words, the ABS 20 and AP 30 may be connected toeach other via wired or wireless connections over a backbone network.

In particular, as illustrated in FIGS. 1C and 1D, the AP interlockingwith the ABS via the Over-The-Air (OTA) may be expressed as a“coordinated AP (C-AP)” or “Enhanced AP”.

Hereinafter, the logical structure and operation mode of a C-AP forallowing a multi-RAT terminal to simultaneously transmit and receivedata via both a cellular network and WLAN will be described in detailwith reference to FIGS. 2 through 5.

FIG. 2 is a view illustrating the logical structure of a C-AP accordingto an embodiment of the present disclosure.

Referring to FIG. 2, the C-AP may include at least one of an 802.11PHY/MAC entity, a coordination function entity, an 802.16 PHY/MACentity, an 802.11 control/RRM entity, a data plane, GLL, and a controlplane. As illustrated in FIG. 2, it is seen that C-AP is interlockedwith the ABS via the 802.16 PHY/MAC and control plane.

FIGS. 3 through 5 illustrate a control and data flow for performingcommunication with a cellular system and WLAN according to the operationmode of C-AP.

First, FIGS. 3A and 3B are structural views illustrating a multi-RATsystem when the C-AP is operated in a wireless backhaul mode.

The wireless backhaul mode is a mode in which WLAN is connected to amulti-RAT terminal, and connected to a cellular network via wirelessbackhaul for operation.

Referring to FIGS. 3A and 3B, it is seen that the C-AP performs datacommunication with a multi-RAT terminal, and communication between theC-AP and the multi-RAT terminal is controlled by the ABS.

FIG. 4 is an example of the structural view illustrating a multi-RATsystem when the C-AP is operated in a converged gateway mode.

The converged gateway mode is a mode in which a multi-RAT terminal isconnected to both WLAN and a cellular system, and connected to a wiredIP backhaul for operation.

Referring to FIG. 4, it is seen that a multi-RAT terminal simultaneouslytransmits and receives data corresponding to 802.11 and 802.16 with theC-AP.

FIGS. 5A and 5B are structural views illustrating a multi-RAT systemwhen the C-AP is operated in coordinated AP mode.

Referring to FIGS. 5A and 5B, a multi-RAT terminal may transmit andreceive data via the C-AP and ABS, respectively. Here, the ABS transmitsand/or receives control signals to and/or from the C-AP via the 802.16PHY/MAC entity (or 802.11 coordination function entity) to control theC-AP. In other words, the ABS and C-AP are interlocked with each otherto perform data communication with the multi-RAT terminal.

Furthermore, the multi-RAT terminal may perform data communication withC-AP using a virtual carrier. The virtual carrier may refer to a carrierdistinguished from a carrier via which the multi-RAT terminal performsdata communication with the ABS.

Hereinafter, an interlock (or coordination) procedure between the ABSand C-AP and coordination functions enabled due to this procedure, and astandard issue related to the C-AP in a multi-RAT system will bedescribed.

1. Access Information can be Shared

A C-AP can have a relation with the ABS including the C-AP via an 802.16link. Accordingly, the C-AP is turned on and then searches an ABS thatcan be communicated with. Subsequently, when the ABS is searched, thenthe C-AP registers the C-AP to the ABS. Through an interaction betweenthe C-AP and ABS, the ABS can make a list of C-APs within the coverageof the ABS without assistance of a network operator.

Furthermore, the C-AP can receive information, such as locationinformation, neighbor AP information, a wireless configurationparameter, and the like, from the ABS. Furthermore, the mobility of WLANcontrolled by the ABS may be implemented via interlock between the ABSand C-AP.

The ABS may provide access information on the APs of the WLAN to amulti-RAT terminal connected to the ABS through information exchangedbetween the ABS and C-AP. The multi-RAT terminal can reduce powerconsumption for detecting the APs of the WLAN through the accessinformation received from the ABS.

Furthermore, the C-AP may provide access information on the ABS to amulti-RAT terminal. In this case, fast handover between the ABS and APcan be carried out.

2. Frame Correspondence (or Alignment) Between ABS and C-AP

Frame timings between the ABS and AP are allowed to correspond to eachother to facilitate an interlock between the ABS and C-AP, and alleviateinter-AP interference. When a beacon signal broadcast by the C-APcorresponds to a DL sub-frame of the ABS, a multi-RAT terminal is notnecessarily required to use a CLC mode to receive a beacon.

Furthermore, a beacon timing distributed between C-APs may have a smallsearch interval for frame timing correspondence between the ABS andC-AP. Through this, multi-RAT terminal can easily detect beacons.

3. Inter-AP Coordination

The management function for Inter-AP Protocol (IAPP) and multiple APenvironments may be supported in the standard of 802.11f/v.

Since neighbor APs may use different frequency channels, it may bedifficult to communicate between the neighbor APs. Here, the ABS may bea hub for communication between the APs, and may be a central controllerto control all the APs.

The ABS having such a communication link may provide the followingflexibility to a WLAN network.

(1) Coordinated Dynamic Channel Switching

The base station may allow the C-AP to be switched to a frequencychannel having the least channel interference to transmit data.

(2) Coordinated Dynamic Adjustment of Transmission Power

Currently, APs may be configured to transmit data at the maximum powerall the time, but through this, the transmission power of the C-AP canbe adjusted according to the location and interference level of neighborC-APs.

(3) Coordinated Dynamic Timing Adjustment

The beacon transmission timings of C-APs may be configured to differfrom one another to prevent collision while transmitting beacon signals,and thus the terminal can receive the beacon signals of several C-APslocated in the vicinity with no collision.

(4) Coordinated Capacity Sharing Among APs

It may be possible to make a control such that several terminals aredispersed to access neighbor C-APs according to a current load conditionof each C-AP.

4. Converged QoS/Connection Management

Converged security and IP flow mobility has been discussed in thestandard, but a discussion of coordination between the ABS and C-AP hasbeen limited.

A cellular network and WLAN can share the context and security of amulti-RAT terminal, and provide easier interworking for QoS andconnection management through this.

(1) QoS/Connection Management

-   -   Prioritized AMS scheduling, QoS provisioning for off-loading

(2) IP Flow

-   -   Integrated security association, IP flow mobility support

5.C-AP related standard issues

(1) Protocols Between ABS and C-AP

A new MAC control message may be defined to transmit and receive aconfiguration parameter and a negotiation parameter between the ABS andC-AP.

In other words, a registration MAC message may be defined to registerthe C-AP to the ABS.

Furthermore, a configuration MAC message may be defined to configure theC-AP (for example, AP power, timing, operation mode, etc.).

Furthermore a C-AP report MAC message may be defined to report to theABS (neighbor AP scan report, interference report, data load report,etc.).

Furthermore, an MAC message related to the mobility support of amulti-RAT terminal may be defined.

Otherwise, such a control message may be transmitted and received byusing Non-Access Stratum (NAS) or a control plane message.

(2) Protocols Between ABS and Multi-RAT Terminal

The following procedure may be necessarily required to be definedbetween the ABS and multi-RAT terminal to provide a higher level ofmulti-RAT operation of the multi-RAT terminal.

1) Multi-RAT mobility support (scanning, neighbor advertisement message,etc.)

2) Multi-RAT management (configuration, active, turn-off, power, etc.)

3) IP/security binding

Such a process may be also enabled through an MAC message, and may bealso configured through an upper level message or NAS message such asOMA DM.

Hereinafter, a method in which the ABS and C-AP proposed in the presentdisclosure are interlocked with each other based on the foregoingdescription to allow a multi-RAT terminal to transmit and receive datathrough the ABS and C-AP will be described in detail.

FIGS. 6 through 9 illustrates a case that a multi-RAT terminal accessesa cellular network via a primary network, and accesses WLAN AP via asecondary network.

FIG. 6 is a flow chart illustrating a data communication method of amulti-RAT terminal in a multi-RAT network according to an embodiment ofthe present disclosure.

First, a multi-RAT terminal performs a network (re)entry procedure withthe ABS (S610). The multi-RAT terminal notifies that it has thecapability of accessing WLAN, namely, it is a terminal supportingmulti-RAT, through the network (re)entry procedure to the ABS.

Subsequently, the ABS transmits information required for the multi-RATterminal to access an AP within the ABS coverage to the multi-RATterminal (S620). Here, the ABS can transmits information on an AP or APgroup that can be accessed by the multi-RAT terminal based on areceiving signal level or location of the multi-RAT terminal to themulti-RAT terminal. In other words, the ABS may transmit a Service SetIDentifier (SSID) of the AP, an MAC address, a WEP key, a channel number(frequency information), frequency hopping information, a protocolversion (11a/b/n . . . ) of the AP, timing offset information between abeacon and a base station frame, and the like, to the multi-RATterminal.

Here, timing offset information between a beacon frame and an inter-ABSframe is transmitted to synchronize an ABS frame and a C-AP beaconframe, thereby allowing a multi-RAT terminal to easily find a beaconframe using a relative position of the frame timing of the base stationcurrently being accessed to reduce the power consumption of themulti-RAT terminal.

Here, the ABS may transmit a relative location of the beacon frame byexpressing it as a difference from a specific frame time.

For example, a beacon transmission period transmitted by the C-AP may besame as a superframe period of IEEE 802.16m, and moreover, when severalAPs are set to have an offset different from the same period, it may bealso possible to solve the interference problem.

In particular, when the transmission and reception timings of a beaconframe are well adjusted at the ABS and C-AP, it may be possible to solvethe co-located co-existence problem occurred in the terminal. In otherwords, the multi-RAT terminal does not perform uplink transmission tothe ABS while the multi-RAT terminal receives key information (such asbeacon, etc.) through a wireless LAN. For example, if C-AP beacon andABS superframe header (BCH) transmission times are the same, a multi-RATterminal may receive both two information without interference.

Here, assuming that the ABS is an IEEE 802.16 or LTE system, it has aframe period of 5 ms and 10 ms, respectively, but in case of WLAN, ithas mostly a beacon transmission period of 102.4 ms. In this case, theABS and AP are frame-synchronized every 2560 ms.

Here, the ABS notifies each beacon transmission timing of AP in relationwith a current frame in a frame offset form to the multi-RAT terminal,thereby allowing the multi-RAT terminal to minimize a time of scanningAPs.

Furthermore, the multi-RAT terminal may know the beacon frameinformation of a neighbor AP located in the vicinity of a currentlyaccessed AP from the ABS, and scan a beacon signal of the neighbor APeven in the state of currently accessing AP. In order to avoid inter-APinterference, the ABS may notify a beacon transmission timing of theneighbor AP to each AP, and each AP may not transmit data at thecorresponding timing, thereby avoiding interference.

Furthermore, the procedure of allowing the C-AP to make registrationwith the ABS may be as follows.

First, an interlock operation between the ABS and C-AP can be carriedout in the following two schemes.

(1) The C-AP has its own wired backhaul to transmit and/or receive onlycontrol information to and/or from a cellular system via a wireless linkwith respect to the ABS.: Virtual Carrier Scenario

(2) The C-AP operates like a multi-RAT relay to transmit and/or receiveboth control information and relayed data to and/or from the ABS via awireless link.: Enhanced Tethering Scenario

Also, the procedure of allowing the C-AP to register to the ABS may beas follows.

The C-AP performs the procedure of registering to the ABS when amulti-RAT network is found, namely, when an ABS that can be interlockedwith the C-AP itself is found.

The C-AP accesses a cellular system to register the C-AP itself prior toactivating a wireless LAN. Otherwise, even when the C-AP has beenactivated, the C-AP itself may be registered to a cellular system havinga higher coverage.

The procedure of registering the C-AP to the ABS may be carried out byexchanging an MAC message between the ABS and C-AP, or implemented eventhrough a higher message. Here, information exchanged through the MACmessage may be transmitted to a management entity of the ABS ortransmitted to a network entity managing interworking.

Here, the C-AP may transmit its own various information to the ABS. Inother words, the C-AP may transmit configuration information or the liketo the ABS, and the ABS may notify the information of the C-AP tomulti-RAT terminals within the ABS coverage based on this.

Otherwise, the ABS may notify registration procedure-related informationdirectly to the C-AP without using transmission and reception betweenthe ABS and C-AP. In other words, a provider may add the correspondingfunction to the C-AP similarly to a femto base station, therebyautomatically assigning all configurations of the C-AP.

In particular, when the C-AP has its own location information by itself(through LBS, GSS, etc.), the C-AP may send its own location informationto the ABS while performing a registration procedure to the ABS.Otherwise, the ABS may receive measurement information related to thelocation of the C-AP through a technology such as LBS or the like.

Furthermore, the ABS may instruct the C-AP to scan neighbor APs toreceive the information of other APs located in the vicinity of theC-AP. Through this, the ABS may estimate a relative location betweenAPs.

Furthermore, providers may know the location of an AP or the likethrough AP information or the like received from the ABS, therebyestimating the location information of a terminal accessing thecorresponding AP on the Internet. For example, it may be used to knowthe location information of an IP phone in E911 or the like.

Subsequently, the multi-RAT terminal measures a beacon of AP accordingto the information received from the ABS (S630), and notifies whether ornot an access to the AP is available to the ABS (S640). In this case,the multi-RAT terminal measures a receiving signal level for a beacon ofthe AP, thereby determining whether or not an access to the AP isavailable.

Here, the method of allowing a multi-RAT terminal to scan APs will bedescribed in detail.

The multi-RAT terminal may consume a lot of time and power to find APswhen the multi-RAT terminal does not have any previous information onAPs.

Accordingly, the C-AP may transmit a specific signal to a cellularnetwork at a specific timing to allow the multi-RAT terminal to performcellular communication with the ABS as well as find the C-AP. Themulti-RAT terminal may measure the specific signal at a predeterminedtime to check whether there exists any currently accessible WLAN AP inthe vicinity. Here, the specific signal refers to a signal to identifyan AP.

For example, there is a case where the ABS does not transmit a preambleat a specific timing to reinforce a location measurement function inIEEE 802.16m, and at this timing, APs may transmit a predeterminedsignal. Here, the predetermined signal is a signal negotiated in advancewith the ABS, which is a signal to know whom the C-AP is based on thekind of signal and transmission timing. The predetermined signal mayhave a specific pattern based on a location of AP, a frequency band usedor the like, and thus if the multi-RAT terminal receives this signal andthen reports the received information to the ABS, then the ABS may senda suitable AP list to the multi-RAT terminal.

In particular, when a transmission signal is provided to have 9different patterns and discern 9 channels in the 2.4 GHz WLAN band, themulti-RAT terminal may receive the corresponding signal and then searchonly the corresponding one WLAN channel. In this case, the multi-RATterminal can reduce power consumption for AP scanning.

Furthermore, in addition to the preamble, it may be also possible thatthe ABS makes a promise not to send a signal to a specific point at apredetermined time, and then allows the C-AP to transmit a predeterminedsignal to the specific point. In this case, a data transmission pointfor the C-AP may be notified to the multi-RAT terminal via A-MAP orPDCCH. In this case, the ABS can previously assign STID or C-RNTI forC-AP assignment, and then transmit A-MAP or PDCCH CRC masked with thisvalue to the multi-RAT terminal.

Furthermore, the ABS may allow the C-AP to transmit data, and each C-APtherein to encode its own information (for example, beacon information),thereby transmitting a specific resource. In this case, the ABS cannotify a data transmission point for the C-AP via A-MAP or PDCCH. Inthis case, the ABS can previously assign STID or C-RNTI for C-APassignment, and then transmit A-MAP or PDCCH CRC masked with this valueto the multi-RAT terminal. Accordingly, the multi-RAT terminal maydecode a specific burst at a specific point, thereby checkinginformation on neighbor APs.

Subsequently, in case that the receiving level of AP is greater than apredetermined value (or threshold value), the ABS transmits detailaccess information to the multi-RAT terminal, thereby allowing themulti-RAT terminal to access the AP (S650).

Subsequently, the multi-RAT terminal performs an access procedure withthe AP (S660).

Here, the process of allowing the multi-RAT terminal to access an APunder the control of the ABS according to various schemes of themulti-RAT terminal for searching an AP will be described through thefollowing embodiments.

First Embodiment

According to a first embodiment, there is provided a method of allowingthe multi-RAT terminal to search an AP by itself to access the AP.

FIG. 7 is a flow chart illustrating the first embodiment.

First, in case that a multi-RAT terminal wants to access an AP due tovarious reasons, the multi-RAT terminal transmits an access requestmessage for requesting an access to the AP to the ABS (S710).

Subsequently, the ABS transmits a response message including informationon AP candidates that can be accessed by the multi-RAT terminal to themulti-RAT terminal according to the status of the multi-RAT terminal(location, battery, signal intensity, etc.) (S720). Here, the responsemessage is a message corresponding to the access request message of themulti-RAT terminal.

Subsequently, the multi-RAT terminal searches (scans or monitors) an APbased on the received response message (S730).

Subsequently, the multi-RAT terminal reports a measurement result of theAP to the ABS (S740).

Subsequently, the ABS transmits detail information required for AP(target AP) assignment and an access to the AP to the multi-RAT terminalusing the AP measurement result received from the multi-RAT terminal(S750).

Subsequently, the multi-RAT terminal performs an access procedure withthe target AP according to the guide of the ABS (S760).

Second Embodiment

According to a second embodiment, there is provided a method of allowinga multi-RAT terminal to access a specific AP when the AP has beenpreviously searched.

FIG. 8 is a flow chart illustrating the second embodiment.

The multi-RAT terminal transmits information on the searched APs to theABS (S810, S820). At this time, the multi-RAT terminal may transmitvarious information (SSID, measurement information, etc.) related to thesearched APs to the ABS.

Subsequently, when the APs received from the multi-RAT terminal includesan AP enabled with a coordination operation with the ABS (C-AP), the ABSinstructs the multi-RAT terminal to access the AP, and transmits detailinformation required for accessing the AP to the multi-RAT terminal(S830).

Subsequently, the multi-RAT terminal accesses a target AP according tothe guide of the ABS (S840).

Third Embodiment

According to a third embodiment, there is provided a method of allowinga multi-RAT terminal to access an AP when the ABS instructs themulti-RAT terminal to search the AP according to the circumstances ofthe terminal.

FIG. 9 is a flow chart illustrating the third embodiment.

First, the ABS transmits an instruction message for instructing thesearch of an AP to the multi-RAT terminal to disperse a load for ABStraffic by taking the status/performance (location, signal intensity,battery, etc.) of the multi-RAT terminal into consideration (S910).Here, the instruction message may include information on candidate APs.

Subsequently, the multi-RAT terminal searches accessible APs based onthe instruction message (S920).

Subsequently, the multi-RAT terminal reports a measurement result of theAPs to the ABS (S930), and the ABS transmits detail information requiredfor target AP assignment and access to allow the multi-RAT terminal toaccess the target AP on the basis of the measurement result receivedfrom the multi-RAT terminal (S940).

Subsequently, the multi-RAT terminal accesses the target AP according tothe guide (or control) of the ABS through an access procedure (S950).

When a multi-RAT terminal has completed an access to AP through thefirst through third embodiments, the multi-RAT terminal transmits accessinformation for the accessed AP to the ABS (S670). Here, accessinformation on the accessed AP may include an IP address assigned byWLAN.

Subsequently, the ABS registers an IP address of the AP accessed by themulti-RAT terminal to a home agent, and binds a WLAN IP with a cellularIP to implement IP mobility.

If a home agent can control the IP assignment of the WLAN AP, a reservedIP among the IP region of WLAN may be previously assigned to themulti-RAT terminal, and thus the multi-RAT terminal can access WLANusing the previously assigned IP address. In other words, when themulti-RAT terminal wants to transmit data via uplink, the ABS mayinstruct the multi-RAT terminal to transmit uplink date to the WLAN APby taking QoS of the flow, current load condition of the ABS, resourceefficiency, and the like into consideration.

The above-described embodiments and modification examples may becombined with one another. Accordingly, each embodiment may not beimplemented as a single but implemented in combination with one anotherwhen the need arises. Such combinations can be easily implemented bythose skilled in the art reading this specification and the combinationsthereof will not be described below in detail. However, even if notdescribed, it should be understood that the combinations thereof willnot be excluded from the present invention, and still fall within thescope of the present invention.

The foregoing embodiments and modification examples may be implementedthrough various means. For example, the embodiments of the presentdisclosure may be implemented by hardware, firmware, software, or anycombination thereof.

In case of a hardware implementation, a method according to theembodiments of the present disclosure may be implemented by one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers, microprocessors, orthe like.

In case of a firmware or software implementation, a method according tothe embodiments of the present disclosure may be implemented in the formof a module, procedure, function, or the like, which performs thefunctions or operations as described above. The software codes may bestored in a memory unit to be driven by a processor. The memory unit maybe located at an inner or outer portion of the processor to send and/orreceive data to and/or from the processor by various publicly-knownmeans.

For example, the method according to the present invention as describedabove may be implemented by software, hardware, or a combination ofboth. For example, the method according to the present invention may bestored in a storage medium (for example, internal memory, flash memory,hard disk, and so on), and may be implemented through codes orinstructions in a software program that can be performed by a processor(for example, internal microprocessor). It will be described withreference to FIG. 10.

FIG. 10 is an internal block diagram illustrating a terminal and a basestation in a multi-RAT system to which an embodiment of the presentdisclosure is applicable.

The terminal 10 may include a controller 11, a memory 12, and a radiofrequency (RF) unit 13.

The terminal 10 may be fixed or have mobility, and may be referred to asanother terminology, such as a user equipment (UE), a user terminal(UT), a subscriber station (SS), a wireless device, an advanced mobilestation (AMS), or the like. Furthermore, the terminal may include themulti-RAT terminal.

In addition, the terminal may include a display unit, a user interface,and the like.

The controller 11 implements a proposed function, process and/or method.The layers of a wireless interface protocol may be implemented by thecontroller 11.

The memory 12 is connected to the controller 11 to store a protocol orparameter for performing wireless communication. In other words, aterminal drive system, applications and general files are storedtherein.

The RF unit 13 is connected to the controller 11 to transmit and/orreceive radio signals.

Incidentally, the display unit can display various information of theterminal, and use a well-known element such as a liquid crystal display(LCD), organic light emitting diodes (OLEDs), and the like. The userinterface can be made of a combination of well-known user interfacessuch as a keypad, a touch screen, or the like.

The base station 20, 30 may include a controller 21, a memory 22, and aradio frequency (RF) unit 23.

Here, the base station 20, 30 may generally refer to a fixed stationthat communicates with the terminal and may be called anotherterminology, such as a NodeB, a base transceiver system (BTS), an accesspoint, and the like. One or more cells may exist within the coverage ofthe base station.

The controller 21 implements a proposed function, process and/or method.The layers of a wireless interface protocol may be implemented by thecontroller 21.

The memory 22 is connected to the controller 21 to store a protocol orparameter for performing wireless communication.

The RF unit 23 is connected to the controller 21 to transmit and/orreceive radio signals.

The controller 11, 21 may include an application-specific integratedcircuit (ASIC), other chip sets, a logic circuit and/or a dataprocessing device. The memory 12, 22 may include read-only memory (ROM),random access memory (RAM), flash memory, memory card, storage mediumand/or other storage devices. The RF unit 13, 23 may include a basebandcircuit for processing radio signals. When the embodiment is implementedby software, the foregoing technique may be implemented by a module(process, function, etc.) performing the foregoing function. The modulemay be stored in the memory 12, 22, and implemented by the controller11, 21.

The memory 12, 22 may be located inside or outside the controller 11,21, and connected to the controller 11, 21 using various well-knownmeans.

It should be noted that technological terms used herein are merely usedto describe a specific embodiment, but not to limit the presentinvention. Also, unless particularly defined otherwise, technologicalterms used herein should be construed as a meaning that is generallyunderstood by those having ordinary skill in the art to which theinvention pertains, and should not be construed too broadly or toonarrowly. Furthermore, if technological terms used herein are wrongterms unable to correctly express the concept of the invention, thenthey should be replaced by technological terms that are properlyunderstood by those skilled in the art. In addition, general terms usedin this invention should be construed based on the definition ofdictionary, or the context, and should not be construed too broadly ortoo narrowly.

Incidentally, unless clearly used otherwise, expressions in the singularnumber include a plural meaning. In this application, the terms“comprising” and “including” should not be construed to necessarilyinclude all of the elements or steps disclosed herein, and should beconstrued not to include some of the elements or steps thereof, orshould be construed to further include additional elements or steps.

Furthermore, in the present disclosure, the terms including an ordinalnumber such as first, second, etc. can be used to describe variouselements, but the elements should not be limited by those terms. Theterms are used merely for the purpose to distinguish an element from theother element. For example, a first element may be named to a secondelement, and similarly, a second element may be named to a first elementwithout departing from the scope of right of the invention.

In case where an element is “connected” or “linked” to the otherelement, it may be directly connected or linked to the other element,but another element may be existed therebetween. On the contrary, incase where an element is “directly connected” or “directly linked” toanother element, it should be understood that any other element is notexisted therebetween.

In the foregoing embodiments, the constituent elements and features ofthe present disclosure are combined with one another in a predeterminedform. Each constituent element or feature thereof should be consideredto be selective as unless otherwise particularly specified. Eachconstituent element or feature thereof may be implemented in a form thatis not combined with any other constituent elements or features.Furthermore, an embodiment of the present disclosure may be alsoconfigured by combining some of the constituent elements and/orfeatures. The sequence of the operations described in the embodiments ofthe present disclosure may be changed. Some of the configurations orfeatures of any embodiment may be included in any other embodiments, ormay be replaced with the configurations and features corresponding tothe any other embodiments. In addition, it will be apparent that anembodiment may be configured by a combination of claims cited by eachother and a new claim may be included by the amendment after filing theapplication.

What is claimed is:
 1. A method for simultaneously communicating datavia a first base station supporting a first radio access technology(RAT) and a second base station supporting a second RAT in a radioaccess system supporting multiple RAT (multi-RAT), the methodcomprising: allowing the first base station to perform a registrationprocedure with the second base station; and allowing the first basestation to transmit control information required for accessing thesecond base station to a terminal supporting multi-RAT (multi-RATterminal), wherein the control information comprises beacon frametransmission timing information for the second base station, and thebeacon frame transmission timing is maintained in transmission timing ofa downlink frame or downlink sub-frame of the first base station withrelative timing offset interval, wherein the relative timing offsetinterval indicates an interval between a downlink frame or downlinksub-frame of the first RAT and a beacon frame of the second RAT tosynchronize the downlink frame or downlink sub-frame of the first RATand the beacon frame of the second RAT, wherein the simultaneouscommunication of data via the first base station and the second basestation occurs under control of a cellular network without switchingmechanism in the multi-RAT terminal, and wherein the first RAT is aradio access technology supporting a cellular system, and the second RATis a radio access technology supporting a wireless local area network(WLAN).
 2. The method of claim 1, wherein the first base station and thesecond base station are connected to each other over wired or wirelessconnections.
 3. A method for allowing a multiple radio access technology(RAT) (multi-RAT) terminal to simultaneously communicate data via afirst base station supporting a first RAT and a second base stationsupporting a second RAT in a radio access system supporting multi-RAT,the method comprising: performing data communication via a first carrierwith the first base station; receiving control information required foraccessing the second base station from the first base station;performing a scanning procedure for at least one second base stationlocated in the vicinity of the first base station based on the controlinformation; performing an access procedure with the second basestation; and performing data communication via a second carrier with theaccessed second base station, wherein the control information comprisesbeacon frame transmission timing information for the second basestation, and the beacon frame transmission timing is maintained intransmission timing of a downlink frame or downlink sub-frame of thefirst base station with relative timing offset interval, wherein therelative timing offset interval indicates an interval between a downlinkframe or downlink sub-frame of the first RAT and a beacon frame of thesecond RAT to synchronize the downlink frame or downlink sub-frame ofthe first RAT and the beacon frame of the second RAT, wherein thesimultaneous communication of data via the first base station and thesecond base station occurs under control of a cellular network withoutswitching mechanism in the multi-RAT terminal, and wherein the first RATis a radio access technology supporting a cellular system, and thesecond RAT is a radio access technology supporting a wireless local areanetwork (WLAN).
 4. A method for simultaneously communicating data via afirst base station supporting a first radio access technology (RAT) anda second base station supporting a second RAT in a radio access systemsupporting multiple RAT (multi-RAT), the method comprising: allowing thesecond base station to perform a registration procedure with the firstbase station; allowing the second base station to transmit a beaconframe to a terminal supporting multi-RAT (multi-RAT terminal);performing an access procedure with the multi-RAT terminal; andperforming data communication via a virtual carrier with the multi-RATterminal; wherein a transmission period of the beacon frame and atransmission period of a downlink frame or downlink sub-frame of thefirst base station have relative timing offset interval, and the virtualcarrier is distinguished from a carrier performing data communicationbetween the first base station and the multi-RAT terminal, wherein therelative timing offset interval indicates an interval between a downlinkframe or downlink sub-frame of the first RAT and a beacon frame of thesecond RAT to synchronize the downlink frame or downlink sub-frame ofthe first RAT and the beacon frame of the second RAT, wherein thesimultaneous communication of data via the first base station and thesecond base station occurs under control of a cellular network withoutswitching mechanism in the multi-RAT terminal, and wherein the first RATis a radio access technology supporting a cellular system, and thesecond RAT is a radio access technology supporting a wireless local areanetwork (WLAN).
 5. The method of claim 4, wherein said performing aregistration procedure comprises: searching a first base station capableof communicating with the second base station; and registering to thesearched first base station using an MAC message.
 6. The method of claim4, wherein information required for an access to the multi-RAT terminalis exchanged with the first base station through the step of performingthe registration procedure.
 7. The method of claim 4, wherein the firstbase station and the second base station are connected to each otherover wired or wireless connections.
 8. A multiple radio accesstechnology (RAT) (multi-RAT) terminal for simultaneously communicatingdata via a first base station supporting a first RAT and a second basestation supporting a second RAT in a radio access system supportingmulti-RAT, the terminal comprising: a wireless communication unitconfigured to transmit and/or receive wireless signals to and/or fromthe outside; and a controller connected to the wireless communicationunit, wherein the controller controls to perform data communication viaa first carrier with the first base station, controls the wirelesscommunication unit to receive control information required for accessingthe second base station from the first base station, controls to performa scanning procedure for at least one second base station located in thevicinity of the first base station based on the control information,controls to perform an access procedure with the second base station,and controls the wireless communication unit to perform datacommunication via a second carrier with the accessed second basestation, wherein the control information comprises beacon frametransmission timing information for the second base station, and thebeacon frame transmission timing is maintained in transmission timing ofa downlink frame or downlink sub-frame of the first base station withrelative timing offset interval, wherein the relative timing offsetinterval indicates an interval between a downlink frame or downlinksub-frame of the first RAT and a beacon frame of the second RAT tosynchronize the downlink frame or downlink sub-frame of the first RATand the beacon frame of the second RAT, wherein the simultaneouscommunicating of data via the first base station and the second basestation occurs under control of a cellular network without switchingmechanism in the multi-RAT terminal, and wherein the first RAT is aradio access technology supporting a cellular system, and the second RATis a radio access technology supporting a wireless local area network(WLAN).
 9. The terminal of claim 8, wherein the first base station andthe second base station are connected to each other over wired orwireless connections.